The present invention relates to an organic electroluminescent device (hereinafter referred to as xe2x80x9corganic EL devicexe2x80x9d), and more particularly, to an organic EL device having an improved seal structure.
C. W. Tang has disclosed a new organic EL device in Japanese Patent Application Laid-Open (kokai) No. 57-51781, and since then, techniques relating to organic EL devices have been developed rapidly, realizing production of EL devices providing high-luminance, bright images and production of multi-color EL devices. However, these EL devices have a disadvantageously short service life, leaving a drawback to be solved.
Techniques for attaining organic EL devices of long service life are focused mainly on the following points: development of highly durable organic compounds, and improvement in seal technique for preventing intrusion of outside contaminants, particularly moisture and oxygen. As is well known, when the moisture which has intruded into an organic EL structure migrates from faults of the cathode surface into a combination comprising an organic substance layer sandwiched by a pair of electrodes, delamination between the organic substance layer and the cathode occurs, resulting in generation of dark spots (black spots); i.e., sites where light emission cannot be attained, due to failure of electrical conduction.
In order to suppress the aforementioned generation of dark spots, intrusion of moisture into the organic EL structure must be prevented. Conventionally, there have been developed several organic EL devices equipped with means for preventing intrusion of moisture into the organic EL structure; such as an organic EL device in which a protective layer containing a desiccant and a seal layer are laminated to the outside of a combination comprising an anode, an organic substance layer, and a cathode, these elements being laminated (Japanese Patent Application Laid-Open (kokai) No. 7-169567), and an organic EL device including a combination formed of a pair of electrodes with an organic substance layer sandwiched therebetween, which combination is accommodated in an airtight casing for sealing where drying means such as barium oxide, calcium oxide, calcium sulfate, or calcium chloride is provided in such a manner that they do not contact the combination (Japanese Patent Application Laid-Open (kokai) No. 9-148066).
However, the aforementioned conventional organic EL devices cannot sufficiently prevent intrusion of moisture into their organic EL structures. Specifically, in both the aforementioned organic EL device in which a protective layer containing a desiccant is laminated to the outside of the structure and in the aforementioned organic EL device including drying means provided in a airtight casing, moisture which has intruded into the organic EL device cannot be sufficiently absorbed in a desiccant, leading to intrusion of moisture into the organic EL structure and disadvantageously generating dark spots.
The present invention has been accomplished to overcome the aforementioned drawbacks, and an object of the present invention is to provide an organic EL device which maintains stable luminescent characteristics for a long period of time by preventing intrusion of moisture into the organic EL structure of the device.
The present inventors have carried out extensive studies in order to attain the aforementioned object, and have found that by forming a combination comprising an insulating layer and a moisture reaction layer, particularly containing a metal having a Pauling""s electronegativity of less than 1.2, on the insulating layer such that the combination covers an organic EL structure comprising an anode, an organic substance layer, and a cathode, the metal is immediately reacted with moisture, to thereby effectively prevent intrusion of moisture into the organic EL structure and short circuits between the organic EL structure and the moisture reaction layer, thereby attaining production of an organic EL device which generates no dark spots and maintains stable luminescent characteristics for a long period of time. The present invention has been accomplished on the basis of this finding.
Accordingly, the present invention provides the following organic EL devices (1) and (2).
(1) An organic EL device having an anode provided on the surface of a transparent substrate, a cathode facing the anode, and an organic substance layer provided between the anode and the cathode and containing a light-emitting layer, characterized in that at least one combination comprising an insulating layer and a moisture reaction layer provided on the insulating layer (insulating layer-moisture reaction layer combination) is provided such that the combination covers an organic EL structure including the organic substance layer, the cathode, and a portion of the anode.
(2) An organic EL device according to (1), wherein the moisture reaction layer contains a metal having a Pauling""s electronegativity of less than 1.2.
Preferably, the present invention employs the following structural features (3) to (9) as shown in the below-described Embodiments.
(3) An organic EL device according to (2), wherein the moisture reaction layer is formed substantially of a metal having a Pauling""s electronegativity of less than 1.2.
(4) An organic EL device according to any one of (1) to (3), wherein an anode insulating layer is provided between the moisture reaction layer and the anode.
(5) An organic EL device according to any one of (1) to (4), wherein a seal substrate is provided above the organic EL structure including the organic substance layer, the cathode, a portion of the anode, and the insulating layer-moisture reaction layer combination, and the seal substrate is fixed to the transparent substrate by use of an adhesive for a seal substrate (the below-described first mode).
(6) An organic EL device according to any one of (1) to (4), wherein the organic EL structure including the organic substance layer, the cathode, a portion of the anode, and the insulating layer-moisture reaction layer combination is molded by use of a seal molding agent (the below-described second mode).
(7) An organic EL device according to any one of (1) to (4), wherein a preliminary moisture reaction layer comprising a water-reactive substance dispersed in a polymer binder is provided over the organic EL structure including the organic substance layer, the cathode, a portion of the anode, and the insulating layer-moisture reaction layer combination, and the preliminary moisture reaction layer is molded by use of a seal-molding agent.
(8) An organic EL device according to (7), wherein the water-reactive substance is at least one metal having a Pauling""s electronegativity of less than 1.2.
(9) An organic EL device according to (7) or (8), wherein the polymer binder is a heat-curable or photo-curable resin.